Sensitizing photographic gelatin



Jan 13, 1959 H. L. TQCHENTKE ErA'L 2,868,661`

sENsI'rIzING PHoToGRAPHIc GELATIN Filed Aug. 4. 1954 LIMED PORK 5mn GEL/WN wim Hmm STEER LlQuoR ADDED MULsloN TYPE: Bon.l

l CONTROL CoNTRoLv+5 ml gf Hoe` H Am LIME STEEP LlQuoR CNTROL 50 mijol Hoe HMQ X LIME STEEP LlQu n A CONTROL +500 ml gfHoe-Hmla L IMESTEEP LIQUolz LIMEn PORK SKIN GELATIN LINES-reap LnQUor-z FROM Cow TAu, STumps ADDED EnULsloN TYDE Bon.

Com-szon. 300 m! Lm:

STEEP LlQuoR FROM Cow TAIL STuMps out according to lthe customary procedures.

United States Patent 2,868,661 SENSITIZING PHOTOGRAPHIC GELATIN Herman L. Tschemke, ehicsgu, .ma Clifford B. saeightif,

Dolton, Illi, assignors to Wilson & C0., Inc., a corporation of Delaware Application August 4, 1954, Serial N o. 447 ,722

Claims. `(Cl. 106-135) The present invention relates to improvements in the preparation of gelatin for photographic use.

In the preparation of sensitive pohotgraphic emulsions having a gelatin base, it is known that the nature of the gelatin employed materially affects the sensitivity of the emulsion, both as regards speed and gradation. Thus, while emulsions prepared with gelatins derived from bone, calf skin .trimmings or mixtures thereof may be employed to produce emulsions of a satisfactory sensitivity, the gelatins produced from dehaired pork skins or pork skin trimmings do not have a satisfactory sensitivity, `areexcessively slow and are lacking in gradation.' In accordance with the present invention, it has been found that the characteristics of gelatins derived from pork skins, either unhaired or dehaired, may be greatly improved as to speed and gradation by the incorporation therein of the constituents derived from the liquors resulting from the steeping with lime of hair-containing materials, such as hogs hair and cow tail stumps. T-he term cow tail stumps is applied Vin packing houses to the cows tails, which have been removed from the animals .and from which the terminal hairs have been removed and from which the meat, bones and fat are also removed.

The invention will be fully understood from the following description, illustrated by the accompanying drawings, in which Fig. 1 presents graphs showing .the effect ,on the sensitivity of a standard yphotographic emulsion of the use of one embodiment ofthe present invention, and Fig. 2 presents a similar graph involving the use of another embodiment of the invention. A

Preliminarily, it may be stated that the photographic characteristics of a gelatin may be determined by employing the gelatin in the preparation of an emulsionaccording to a standard formula, and then determining the sensitivity of the emulsion by any ,of the customary sensitometric procedures, such as those employed in determining the Hurter and Dritfieldmethod, or by the use of a step wedge under standardized conditions. For the purposes of the present application, a procedure employing step wedges has been used and the results have beenexpressed in two ways; either in the form 'of a curve,

plotting density against steps of the sensitometer wedge,

or numerically. In the lattercase, under comparable conditions, Ythe wedge step range indicates the speed of the emulsion and the number of distinctly visible-steps indicates the gradation.

The preparation of the pork skin gelatin may be `carried For example, in a typical operation the pork skins are washed in cold water in vats, each containing about 1000 pounds. After washing with cold water for about 4 hours, about V500 pounds of salt are added and agitation continued for 2 hours. The skins are left in the salt solution for 2 days, agitating once a day, the salt solution drained and the skins washed for 2. hours. The lwashings are rdrained and the skins covered with water and 300 pounds lof vlime added to the vat slowly 'with agitation. `VAfter 2,868,661 Patented Jan. 13, 1959 "ice 10 to 15 days, lthe lime was drained, the skins washed and the process repeated 3 times. After a total of 45 days of lime treatment, the skins are washed for 8 hours. The washings are drained off, the skins again covered with water and the contents ofthe vat are brought to the ldesired pH before cooking by the addition of sulfuric acid, if necessary. The pH is` generally in the range of 3.5 to 7, although it may be as high as 10. Thus by way of example, the steep may be adjusted to a pH of 5.0 with 50 B. sulfuric acid, held at this pH for 96 hours and then Washed until a boil test shows a pH of 5.9 to 6.2. The skins are then drained and are ready for cooking.

The cooking is carried out, as in ordinary practice, in a series of successive stages, known as extractions These are effected at progressively increasing temperatures and for varying times. The gelatinous liquor from each extraction is separately removed and, if desired, may be separately dried; or the liquors from two or more extractions may be mixed and dried together. Thus, the first extraction may be at a temperature of to 140 for 3 to 5 hours; the next at a temperature of 150 to the third at a temperature of 160 to 170; the fourth at a temperature of to 185 and the final extractiongmay be at boiling temperature. The time for theextractions priortowthe last may be approximately the same or may gradually increase andthe final extraction may require 8 to 10 hours. The gel strength of the gelatin secured in the successive extractions, as determined, for example, by the Bloom gelometer, decreases for each extraction and is least for the final extraction. The detailsof'these procedures vary somewhat in different ,plants and in different operations, as to temperature and time for'the different extractions, 'thenuinber employed and the details of the liming procedure. It is to be understood in accordance with the present invention that'the conventional practices of the industry are employed.

In comparing the photographic propertiesl of pork skin gelatins thus'produced in the conventional manner with a. standard gelatin supplied by a manufacturer of sensitized materials, it has been found that the 'emulsions produced from the gelatins from pork skins, and particularly from dehaired pork skins, are very'slow and their gradation is poor, except that the speed of emulsion 'made from gelatin from the last extraction may approximately equal that of the standardgelatin. However, the low gel strength ofthisgelatin makes it unsuitable for use in preparing photographic emulsions, since settling and sedimentation may occur therein.

In accordance with the present invention it has been found that the sensitivity of the pork skin gelatins, b oth as to speed and gradation, may be markedly increased by the addition of lime steep liquor derived from haircontaining materials ,such as hogs hair and cow tail stumps. The amountiernployed may vary. Thus there may be incorporated into the gelatin the steep 'liquor gelatin, but without corresponding improvement in prop-- erty.` Preferably, the proportion of steep liquor used is 'in the range of that equivalent to from 0.01 to 0.05

pound of the hair-containing material per pound ef the gelatin.

The liquor from the hair-containing material, such as the hogs hair or cow tail stumps, is suitably prepared by liming these materials for aperiod'fro-r'n 12 to 65 days or longer in a limev steep containing 6% -lime), with occasional stirring, yand lis thenwithdrawn, filtered or settled' and incorporated in r`'the Agelatinfin the `-pro portions set forth above. Other concentrations of lime may be employed, it being preferred that some excess of undissolved lime be present throughout the steeping period. The sensitizing liquor may be added to the liquors resulting from the cooking out of the pork skins, preferably to one of those resulting from the rst 4 extractions or from mixtures thereof, before the gelatin solution is dried; or dried gelatin from corresponding extractions of the pork skin or mixtures thereof may be remelted, the sensitizing liquor added, and the mixture then dried. As is readily apparent, if desired, the sensitizing liquor may be concentrated or dried, preferably in' vacuo, and the resulting concentrate or solids redissolved inwater for use as the sensitizing material.

The addition of the sensitizing liquor and the incorporation of its contents into the pork skin gelatin greatly increases the speedand gradation of emulsions made therefrom. At the same time, it has been found that it has a tendency to increase the susceptibility of the emulsion to fog. Ingredients of the sensitizing liquors which are the cause of the increased fogging tendency have not been identified. However, in accordance with the present invention it has been found that these ingredients are removed from the sensitizing liquor by contacting the latter with an adsorbent of the class including silica gel and synthetic cation exchangers. The synthetic cation exchangers which have been found suitable for this purpose are the insoluble, infusible copolymers derived from mixtures containing a compound having a polymerizable grouping and at least one other polymerizable grouping of the class consisting of styrene, maleic anhydride, acrylic acid and substituted acrylic acids, as described, for example, in United States Letters Patent 2,340,110 and 2,340,- 111. A suitable commercial resin of this type s that known as Amberlite IR-SO.

Contact of the sensitizing liquor with the adsorbents of the class hereinbefore referred to does not reduce the sensitizing action of the sensitizing materials, but greatly reduces or eliminates the tendency to fogging.

The effectiveness of the sensitizing agents employed in accordance with the present invention has been demonstrated on emulsions both of the boiling type and the ammonia type. As is readily apparent, the emulsions containing the pork skin gelatin and sensitizers in accordance with the present invention may be prepared by any of the procedures employed in the manufacture of photographic materials. For the purpose of determining the action of the materials involved in accordance wit-h the present invention, certain standardized procedures have been adopted in the making of the test emulsions. These are procedures recognized in the photographic industry as typical. They are as follows for a test emulsion of the character known as a boil-type emulsion.

A solution is prepared as follows:

Water cc 400 Potassium bromide gms 72 Potassium iodide gms 3.5 Gelatin gms The temperature of the solution is adjusted to 160 F. and a solution of 100 gms. silver nitrate inA 1000 cc. of water is added at such a rate that 40% is added in the rst minute and the remainder in 25 minutes with constant agitation. Then a solution consisting of 200 gms. of gelatin and 400 cc. Water, adjusted to a pH of 6.5-6.7 and a temperature of 160 F. is added and the emulsion held at 160 F. for 25 minutes. The emulsion is then chilled until it has gelled into slabs and is cut into cubes of from 1b to 3K1" on the side. These are washed with cold water until a solution of the cubes indicates a conductivity of 3500 x 10- mho/cm.

The cubes are melted to 130 F. in 20 minutes and ripened at this temperature for various periods, typical periods being 30 minutes, 70 minutes and 110 minutes. The ripening periods may be varied, but for comparable tests, the ripening periods should be the same.

It will be understood that the procedures employed in preparing the test emulsions may be varied, so long as uniform procedures are employed throughout any series of tests.

In carrying out the tests illustrating the effect of the sensitizing materials hereinafter referred to, it will be understood that in formulating the emulsions by the methods above described, where gelatin is referred to, the gelatin employed is the pork skin gelatin or the pork Skin gelatin with the added sensitizing material, as identified in connection with the various experiments.

In general in the experiments described hereinafter, unless otherwise indicated, the boil type emulsions were employed and the ripening periods are indicated by the letters A, B and C to designate respectively ripening periods of 30 minutes, 70 minutes and 110 minutes.

As hereinbefore indicated, the speed and gradation of the emulsions were determined according to customary procedures, using a standard step wedge having 2l steps, and calibrated according to American Standard Diluse Density Type P2b. The emulsions of a series are exposed -to secure conditions of equal fog on the test strip.

The results are indicated in the following description in either of two ways.

In one method of indication, which is illustrated in the curves shown in Figs. l and 2, the density of the image of each sensitometer step is determined and a curve is drawn by plotting density against sensitometer Steps. In such a curve, the properties of the emulsion are indicated by the shape and the slope Vof the curve in the conventional manner.

In the second method of expression of the results of these tests, the number of wedge steps visible under conditions of equal fog is determined as well as the number of the irst wedge step which is distinctly visible. vThe number of the rst wedge step which is barely visible, but is distinct irrespective of the amount of fog or density, is designated hereinafter as the wedge step range and indicates the speed of the emulsion. An increase of one wedge step is approximately equivalent to about 50% increase in speed. The gradation is indicated by the number of distinctly visible wedge steps as seen when the strip is placed between the eye and the northern sky, as compared with the total wedge step range.

While the methods of test referred to hereinbefore, as used in illustrating the present invention, do not have the degree of precision of other methods known in the industry, they are recognized as adequate to indicate the properties of gelatins used in photographic emulsion manufacture and are recognized as showing the approximate photographic characteristics of the gelatin.

EXAMPLE l A gelatin was prepared from dehaired pork skin trimmings prepared as hereinbefore described. The gelatins from the different runs or extractions were kept separate. In comparison with a standard or control photographic gelatin supplied by a photographicsupply house, using boil type emulsions, the gelatin from the first run was extremely slow in speed and flat in gradation. The gelatin from the second run was 200% slower than the standard and was very at in gradation. The gelatin from the fourth run was slower than the standard gelatin and had somewhat less gradation. The gelatin from the fifth run was equal to the standard in speed and had a slightly steeper gradation. However, gelatins from the fourth and fifth runs, and particularly that from the fifth run, were so low in gel strength as to be substantially unusable on account of sedimentation of the emulsion.

A sensitizing liquor was prepared as follows:

About 5 pounds of hogs hair was limed for 25 days in a 6% lime suspension held at 50 F., the hair being agitated'daily. At the end of this period, one-half 0f the steep liquor (approximatelyll pounds) was drained from the hair, adjusted to a pH of 6.0 withsulfuric acidv and filtered through flter'cell toclarify it. Samples of 2 pounds each of :a gelatin from the rst cook-out of a plant run Vonv pork skin trimmings, made Ias hereinbefore described, was dissolved to a 16% solutionvand varying amounts of the filtered-steep liquor were added. These amounts were respectively 5, 50 and 500 cc. The solutions with the added sensitizing liquor were dried, as was a similar solution to which Vno sensitizing liquor had been added. The resulting gelatins were then dried. Boil type emulsions were prepared from each with ripening periods of 30, 70 and 110 minutes. A sensitometric test was then made by the step wedge method as hereinbefore referred to and the results were plotted. These results are illustrated in the curves shown in Fig. l of the accompanying drawing. In Fig. 1, the numeral 1 designates the curve resulting from the sensitometric test on the emulsion employing the gelatin to which no sensitizing material had been added. The curves 2, 3 and 4 designate respectively the curves showing the results of the sensitometric tests on the emulsions employing the gelatins to which there had been added respectively 5 cc., 50 cc.Y and 500 cc. of the sensitizing liquor. As will be apparent from these curves, the speed and gradation of the emulsions were progressively increased by increasing amounts of the sensitizing liquor.

In these tests, fthe addition of 5 cc. of the sensitizing liquor corresponds to the addition to 1 pound of gelatin of the material derived from 0.0003 pound of the hogs hair; that of 50 cc. to 0.003 pound of hogs hair and that of 500 cc. -to 0.03 pound of hogs hair. A definite improvement in speed and gradation was thus secured by the addition to the liquor of as little as 0.0003 pound of hogs hair per pound of gelatin.

EXAMPLE 2 The gelatin from dehaired pork skin trimmings was prepared as described in Example l.

A sensitizing liquor was prepared as follows:

5 pound portions of cow tail stumps were each placed separately in 40V pounds of a 6% lime suspension. The mixtures lwere agitated daily and kept at 50 F. At the end of 25 days, one-half of the steep liquor was removed from each container separately and replaced with the. equivalent weight of water containing l poundA of lime. At the end of 50 days total steeping time, the steep liquor was again drained off and the solids allowed to settle out. Some of the liquor wasdecanted from the solids, adjusted to an pH of 6.5 and ltered. The steep liquor was added to a 12% solution of the gelatin, produced in the same way as in the preceding example,` in proportions to provide, per pound of gelatin, the lime steep from 0.005 pound of cow tails. A

Boil type of emulsions were prepared fromeach of the'y gelatins Vthus sensitized as in the preceding example, a sensitometric test was made by the step wedge method as hereinbefore referred, and the results were plotted. These results are illustrated in the curve shown in Fig. 2 of the accompanying drawings. In Fig. 2, the numeral 5 designates the curve resulting from the sensitometric test on the emulsion employing the gelatin containing the steep liquor as hereinbefore described. As will be noted on comparison with the curve 1 in Fig. l, the addition of the sensitizing liquor produced a marked increase in both speed and gradation ofthe emulsion EXAMPLE 3 A 20 poundV lot of cow tail stumps was steeped in a 6% lime suspension for a period of 67 days and the steep liquor was drawn off. lIt amounted to 146 pounds. A portion was centrifuged to clarify it. This liquor was added toa solution of a pork skin gelatin in such proportionrthat the extract equivalent to 0.0128r y.pound of the cow tail stumps was supplied for each pound of thefgelatin. lThe resulting mixtureA was dried and an emulsion was prepared from it by the standard procedure and compared with an emulsion prepared from the same gelatin to which no addition had been made, as a control. The results are given in the following tabulation.

(In this tabulation and in those hereinafter set forth, a fog determination lwas made upon an emulsion ripened for 110 minutes. In the data given for speed and gradation the three columns headed A, B and C indicate respectively emulsions having ripening periods of 30, 70

yand 110 minutes.)

Table l Speed Gradation Fog A B C A. B C

contra sught 1o 11 12 1o 11v 12 Treated gelatin Grayish Black 15 14 13 11 10 l0 As will be apparent, the speedA of the emulsion from thegelatinV was materially increased by the addition of the'sensitizingliquor, although in this case the gradation of the emulsion was not improved.

EXAMPLE 4 A V140 pound lot of cowftail stumps was limed 50 days and the lime steep liquor wasA drawn off. It amounted to 220V pounds. Another 140 pound lot of cow tail stumps was'limed 57 days. The lime steep liquor was removed, the stock washed with fresh `water and drained. About gallons of water were then added to the stock and small amounts of concentrated sulfuric acid were added over a 96 hour period, the pH of the steep being gradually brought to 4.5. The acid steep -was then withdrawn. Both steep liquors were` ltered through cloth and were stored at a low temperature (below about 60 F.) for 7 weeks. At the end of this time, quantities of both the lime steep liquor and the acidv steep liquor lwere incorporated in gelatin in amounts correspondingy to 0.0128 pound of the cow tail stumps to each pound of gelatin. The resulting sensitized gelatin was dried and an emulsion prepared from it by the standard procedure described above, an emulsion also being prepared from the untreated gelatin as a control.

The two were compared with the following results:

Table Il Speed Gradatiou Fog- A B C A B C Contro1 sughi: 12 10 12 12 1oV 12 Treated gelatin Dark Grayish. 15 15l 16 15 13 12 A 20 pound lot of hog hair was treated with 6% lime suspension for a period of 81 days. The limevsteep liquor was drawnoif and strained. It mounted to 200 pounds. lThe well drained stock was washed with .300 pounds of water, the, washwater removed .and setaside.4

afeeaeei In each instance, the speed of the emulsions from the gelatin were greatly increased by the addition of the sensitizing liquors and at the same time the frogging tendency was increased.

EXAMPLE 6 In this experiment, the effects of shorter liming time and lower temperature during the steep were studied. 79 pounds of cow tail stumps were placed in containers and 75 pounds of water and 4% pounds of slaked lime were added. The contents of the container were thoroughly mixed and then held at a temperature of 45 to 50 for l2 days. A portion of the lime steep was then removed and filtered through cloth. The remainder of the steep liquor was permitted to remain on the cow tail stumps for a total of 68 days, removed and strained. The twelve day steep liquor was incorporated in a pig skin gelatin in amounts corresponding to the equivalent of 0.0128 pound of cow tail stumps to 1 pound of the .gelatin. The resulting sensitized gelatin was then tested for its photographic characteristics. The pig skin gelatin employed in this experiment was the same as that used in Example 3 and having the characteristics set forth as the control gelatin in Table II. The characteristics of the emulsion prepared from the treated gelatin were as follows:

As will be apparent, the speed of the emulsion prepared from the treated gelatin was materially greater than that from the untreated gelatin and the fogging tendency was only slightly greater.

It has been'found that the sensitizing materials present in the lime steep liquors and wash waters prepared from steep liquors in accordance with the present invention do not have their active sensitizing ingredients removed by ltration through such materials as filter cell, Dicalite or lter carbon. Consequently filtration through such materials may be employed in clarifying the sensi.- tizing liquors, if desired.

It has been found also that the fog forming constituents of the sensitizing liquors prepared in accordance with the present invention may be greatly reduced or substantially entirely removed by contacting the liquors with adsorptive agents of the class consisting of silica gel and synthetic cation exchange resins of the type hereinbefore referred to.

The effect of these adsorptive agents will be apparent from the following examples. In each of these examples the lime steep liquor which was used was that derived from the 68day steeping period described under Example 6 above.

EXAMPLE 7 470 grams of silica gel were transferred to a glass tube of 1%" internal diameter and 24%" high, and washed with distilled water. The water was removed from the silica and 600 ml. of the steep liquor was passed through the column at the rate of about 3 ml. per minute. The

- resulting steep liquor was then incorporated in a gelatin solution as hereinbefore described in two concentrations. In the lower concentration it was added in the amount to give the equivalent of 0.0128 pound of the cow tail stumps per pound of gelatin and in the higher concentration to give the equivalent of 0.038 pound of cow tail stumps per pound of gelatin. Emulsions were prepared according to the standard procedure and tested sensitometrically. A portion of this steep liquor was stored for 28 days and a quantity of this liquor was incorporated in another sample of the same gelatin in the lower concentration above referred to. An emulsion was pre- A pared from this product and similarly tested. The results of these tests were as follows:

It will be apparent by comparison of these tests with those presented in the preceding examples that the effect o'f the sensitizing liquor which has been contacted with the silica gel upon the speed and gradation of the pork skin gelatin is as great as that of the sensitizing liquor which has not been contacted with silica gel, but that the fogging tendency is very greatly reduced.

The method of contacting described above is merely illustrative since any means of securing adequate contact between the silica gel and the sensitizing liquor may be employed. The proportion of silica gel employed is not critical and may suitably vary from 1A the proportion indicated in the foregoing example to two or three times the proportion, with marked elfects in the reduction of the fog resulting from the use of the sensitizing liquor.

EXAMPLE 8 A synthetic cationic exchange resin of the type hereinbefore referred Vto and known commercially as Amberlite IRC-50 was employed. About 300 grams of the resin were suspended in distilled water and transferred to a glass tube 1% in diameter and A261/2 high and the water drained from it with the aid of suction. 200 cc. of steep liquor was passed through the column at the rate of about 2 cc. per minute. The efuent was incorporated in pork skin gelatin from the same batch as that used in the preceding Example 7 in the concentration of 0.0254 pound of cow tail stumps per pound of gelatin. An emulsion was prepared from the resulting sensitized gelatin and sensitometric tests made. The following data was secured: v

Table V1 Speed Gradation v Fog A B O A B C Very sught 12 14v 15 11 12 i2 aaeaeei As in the case of the silica gel, the relative proportion of the adsorptive agent may be widely varied, say from grams to 200 grams per 100 cc. of the steep liquor. However, proportions in excess of those employed in the previous example do not havecorrespondingly improved results. Other resins of the same general type may be employed and are effective in reducing the fogging tendency of the sensitizing liquor.

In the foregoing examples the test emulsions employed have been of the boil-type. It has been found that similar and parallel results are secured with the sensitizing liquors according to the present invention when ammonia-type test emulsions are employed, and also with commercial type of emulsions of Varying speeds and color sensitivities.

Although the present invention has been described in connection with the details of certain specific embodiments thereof, it is not intended that these details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

We claim:

1. The method of producing photographic gelatins of improved sensitivity from alkaline type cooked pork skin gelatin which comprises steeping hair at a temperature in the range between about 45 F. and about 50 F. at atmospheric pressure for a period of between about 12 and about 81 days in an aqueous mixture of lime in which lime is present in quantities between 0.18% and 6% by weight, the ratio of hair to aqueous lime mixture being by weight between about 1:7 and about 1:8, separating the steeped liquor from the undissolved hair, adding the steep liquor substantially free of suspended solids to a solution of alkaline type cooked pork skin gelatin of a sensitivity normally unsatisfactory for use in lphotographic emulsions in quantities introducing per pound of said gelatin the steep liquor derived from steeping between about 0.0003 and about 0.5 pound of hair and removing water from the mixture.

2. The method of claim 1 wherein the hair is hogs hair.

3. The method of claim 1 wherein the hair is the hair of cattle.

4. The method of producing photographic gelatins of improved sensitivity from alkaline type cooked pork skin gelatin which comprises steeping hair at a temperature in the range between about 45 F. and about 50 F. at atmospheric pressure for a period of between about 12 and about 8l days in an aqueous mixture of lime in which lime is present in quantities between about 0.18% and about 6% by weight, the ratio of hair to aqueous lime mixture being by weight between about 1:7 and about 1:8, separating the steeped liquor from the undissolved hair,' clarifying the filtered steep liquor by contact with silica gel, adding the'solids free steep liquor to a solution of alkaline type cooked pork skin gelatin of a sensitivity normally unsatisfactory for use in photographic emulsions in quantities introducing per pound of said gelatin the steep liquor derived from steeping between about 0.0003 and about 0.5 pound of hair and removing water from the mixture.

5. 'Ihe method of producing photographic gelatins of improved sensitivity from alkaline type cooked pork skin gelatin which comprises steeping hair at a temperature in the range between about 45 F. and about 50 F. at atmospheric pressure for a period of between about 12 and about 81 days in an aqueous mixture of lime in which lime is present in quantities between about 0.18% and about 6% by weight, the ratio of hair to aqueous lime mixture being by weight between about 1:7 and about 1:8, separating the steeped liquor from the undissolved hair, clarifying the ltered steep liquor by contact with silica gel, adding the solids free steep liquor to a solution of alkaline type cooked pork skin gelatin of a sensitivity normally unsatisfactory for use in photographic emulsions in quantities introducing per pound of said gelatin the steep liquor derived from steeping between about 0.01 yand about 0.05 pound of hair and removing water from the mixture.

6. A photographic gelatin comprising an alkaline type cooked pork skin gelatin in itself incapable of producing E photographic emulsions of good speed or gradation produced by drying an aqueous solution mixture of said gelatin with clarified steep liquor in quantities introducing per pound of gelatin the steep liquor derived from the steeping of between about 0.0003 and about 0.5 pound of hair, said steep liquor being produced by steeping hair at a temperature in the range between about F. and about 50 F. at atmospheric pressure for a period of between about 12 and about 81 days in an aqueous mixture of lime in which lime is present in quantities between about 0.18% and 6% by weight and the ratio of hair to aqueous lime suspension during steeping being by weight between about 1:7 and about 1:8.

7. A sensitizing material for conversion of alkaline type pork skin gelatin to a photographic gelatin useful for photographic emulsions comprising soluble extractives from the liquor obtained by steeping hair at a temperature in the range between about 45 F. and about 50 F.

at atmospheric pressure for `a period of between about 12 and about 8l days in an aqueousv mixture of lime in which lime is present in quantities between about 0.18%

' and about 6% by weight.

8. A sensitizing material for conversion of alkaline type pork skin gelatin to a gelatin useful for preparation of photographic emulsions comprising soluble extractives from the liquor obtained by steeping hair at a temperature in the range between about 45 F. and about 50 F. at atmospheric pressure for a period of between about 12 `and about 81 days in an aqueous mixture of lime in which lime is present in quantities between about 0.18% and about 6% by weight, the ratio of hair. to aqueous lime suspension during steeping being by weight between about 1:7 and about 1:8 and present in the lime steep after contact with silica gel.

9. The sensitizing material of claim 7 wherein the y extractives are derived from the lime steep of hogs hair.

10. The method of producing photographic gelatins of improved sensitivity from alkaline type cooked pork skin gelatin which comprises steeping hair at a temperature in the range between about 45 F. and about 50 F at atmospheric pressure for a period of between about 12 and about 81 days in an aqueous mixture of lime in which lime is present in quantities between 0.18% and 6% by weight, separating the steep liquor from the undissolved hair, adding steep liquor substantially free of suspended solids to a solution of alkaline type cooked pork skin gelatin of a sensitivity normally unsatisfactory for use in photographic emulsions in quantities introducing per pound of said gelatin the steep liquor derived from steeping between about 0.0003 and about 0.5 pound of hair and removing water from the mixture.

References Cited in the tile of this patent UNITED STATES PATENTS 1,537,939 Dunham May 19, 1925 2,068,626 Newton et al Aug. 8, 1939 2,240,116 Holmes Apr. 29, 1941 2,399,161 Brother et al. Apr. 30, 1946 2,648,659 Spence et al Aug. 1l, 1953 2,743,265 Garono Apr. 24, 1956 OTHER REFERENCES Delmonte: Technology of Adhesives, pages 305-306. 

1. THE METHOD OF PRODUCING PHOTOGRAPHIC GELATINS OF IMPROVED SENSITIVITY FROM ALKALINE TYPE COOKED PORK SKIN GELATIN WHICH COMPRISES STEEPING HAIR AT A TEMPERATURE IN THE RANGE BETWEEN ABOUT 45* F. AND ABOUT 50*F. AT ATMOSPHERIC PRESSURE FOR A PERIOD OF BETWEEN ABOUT 12 AND ABOUT 81 DAYS IN AN AQUEOUS MIXTURE OF LIME IN WHICH LIME IS PRESENT IN QUANTITIES BETWEEN 0.18% AND 6% BY WEIGHT, THE RATIO OF HAIR TO AQUEOUS LIME MIXTURE BEING BY WEIGHT BETWEEN ABOUT 1:7 AND ABOUT 1:8, SEPARATING THE STEEPED LIQUOR FROM THE UNDISSOLVED HAIR, ADDING THE STEEP LIQUOR SUBSTANTIALLY FREE OF SUSPENDED SOLIDS TO A SOLUTION OF ALKALINE TYPE COOKED PORK SKIN GELATIN OF A SENSITIVITY NORMALLY UNSATISFACTORY FOR USE IN PHOTOGRAPHIC EMULSIONS IN QUANTITIES INTRODUCING PER POUND OF SAID GELATIN THE STEEP LIQUOR DERIVED FROM STEEPING BETWEEN ABOUT 0.0003 AND ABOUT 0.5 POUND OF HAIR AND REMOVING WATER FROM THE MIXTURE. 